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The fate of the vast stocks of organic carbon stored in permafrost of the Western Siberian Lowland, the world’s largest peatland, is uncertain. Specifically, the amount of greenhouse gas emissions from rivers in the region is unknown. Here we present estimates of annual CO2emissions from 58 rivers across all permafrost zones of the Western Siberian Lowland, between 56 and 67° N. We find that emissions peak at the permafrost boundary, and decrease where permafrost is more prevalent and in colder climatic conditions. River CO2emissions were high, and on average two times greater than downstream carbon export. We suggest that high emissions and emission/export ratios are a result of warm temperatures and the long transit times of river water. We show that rivers in the Western Siberian Lowland play an important role in the carbon cycle by degassing terrestrial carbon before its transport to the Arctic Ocean, and suggest that changes in both temperature and precipitation are important for understanding and predicting high-latitude river CO2emissions in a changing climate. Rivers in the Western Siberian Lowland, the world’s largest peatland, play a significant role in the release of terrestrial carbon to the atmosphere, according to in situ measurements of carbon dioxide emissions from rivers.

Lakes can store water for long periods of time, which influences the transport of water and hydrologic tracers and changes catchment transit times downstream. However, the impact that the transit time of lakes has on catchment transit times has received little attention to date. We derived water and isotope mass balances for two lakes and examine the use of time‐variant transit time solutions with StorAge Selection functions to estimate the water ages of evaporation and lake outflows. We used the convolution of the StorAge Selection function transit time estimations with inflow transit times to estimate the transit times downstream of each lake. The lakes exhibited contrasting storage effects for discharge; with direct storage effects (newest water exiting during low flow) for a larger lake fed by a small catchment, and inverse storage effects (newest water exiting during high flow) for a smaller lake with a large catchment. The water and isotope mass balance yielded estimates of daily and annual evaporation fluxes, which were similar between the two lakes. The proposed framework is an effective tool to identify the effects of precipitation, surface inflow, and evaporation on the transit times for relatively small, shallow lakes, using a combination of water and isotope mass balance methods. A new method of using transit time distributions of discharge and evaporation to help identify lake mixing and flow pathsEvaporation flux ages are much younger than lake outflows, drawing primarily on young summer inputsCatchments influenced by lakes may yield shorter transit times due to evaporation effects

Atlantic salmon is an economically and ecologically important fish species, whose survival is dependent on successful spawning in headwater rivers. Streamflow dynamics often have a strong control on spawning because fish require sufficiently high discharges to move upriver and enter spawning streams. However, these streamflow effects are modulated by biological factors such as the number and the timing of returning fish in relation to the annual spawning window in the fall/winter. In this paper, we develop and apply a novel probabilistic approach to quantify these interactions using a parsimonious outflux‐influx model linking the number of female salmon emigrating (i.e., outflux) and returning (i.e., influx) to a spawning stream in Scotland. The model explicitly accounts for the interannual variability of the hydrologic regime and the hydrological connectivity of spawning streams to main rivers. Model results are evaluated against a detailed long‐term (40 years) hydroecological data set that includes annual fluxes of salmon, allowing us to explicitly assess the role of discharge variability. The satisfactory model results show quantitatively that hydrologic variability contributes to the observed dynamics of salmon returns, with a good correlation between the positive (negative) peaks in the immigration data set and the exceedance (nonexceedance) probability of a threshold flow (0.3 m3/s). Importantly, model performance deteriorates when the interannual variability of flow regime is disregarded. The analysis suggests that flow thresholds and hydrological connectivity for spawning return represent a quantifiable and predictable feature of salmon rivers, which may be helpful in decision making where flow regimes are altered by water abstractions. We developed a simple, parsimonious outflux‐influx model linking the number of salmon emigrating and returning to the same streamThe model quantitatively accounts for the influence of the interannual variability of flow regime on the hydrological connectivityResults are compared against a detailed long‐term hydroecological data set that includes annual fluxes of salmon and daily discharges

We combined high‐frequency dissolved organic matter fluorescence (FDOM) data with stable isotope observations to identify the sources and ages of runoff that cause temporal variability in dissolved organic carbon (DOC) within a peat‐dominated Scottish catchment. FDOM was strongly correlated (r2∼ 0.8) with DOC, allowing inference of a 15 min time series. We captured 34 events over a range of hydrological conditions. Along with marked seasonality, different event responses were observed during summer depending on dry or wet antecedent conditions. The majority of events exhibited anticlockwise hysteresis as a result of the expansion of the riparian saturation zone, mobilizing previously unconnected DOC sources. Water ages from the main runoff sources were extracted from a tracer‐aided hydrological model. Particularly useful were ages of overland flow, which were negatively correlated with DOC concentration. Overland flow age, which ranged between 0.2 and 360 days, reflected antecedent conditions, with younger water generally mobilizing the highest DOC concentrations in summer events. During small events with dry antecedent conditions, DOC response was proportionally higher due to the displacement and mixing of small volumes of previously unconnected highly concentrated riparian soil waters by new precipitation. During large events with wet antecedent conditions, the riparian saturation zone expands to organic layers on the hillslopes causing peaks in DOC. However, these peaks were limited by dilution and supply. This study highlights the utility of linking high‐frequency DOC measurements with other tracers, allowing the effects of hydrologic connectivity and antecedent conditions on delivery of DOC to streams to be assessed. Stream DOC dynamics are strongly linked to variations in the age of source watersNonstationary flow‐DOC relationships reflect changing hydrologic connectivityFDOM is a reliable proxy for long‐term, high‐resolution DOC time series

Relationships between hydrochemistry and invertebrate assemblages were assessed at fine spatial scales within the hyporheic zone of an upland stream. Eighteen stacked colonisation samplers were placed in the streambed and sampled regularly over an 8-month period. Each stack consisted of three individual sampling chambers, positioned at mean depths of 15, 30 and 45 cm below the bed surface. Each chamber had an internal volume of 600 cm3 and was filled with sediment in the 2–8 mm (b-axis) size range. Water was extracted from each chamber at approximately fortnightly intervals, to characterise its hydrochemistry (dissolved oxygen concentration and alkalinity) and infer the presence of groundwater. Six randomly selected stacks were removed in each of three seasons (winter, spring and summer), with invertebrates present inside then identified and enumerated. Despite marked inter-sample differences in hydrochemistry and the variable presence of groundwater within the hyporheic zone, sampling locations were characterised by broadly similar invertebrate assemblages. Generalised linear mixed models indicated that inter-sample differences in assemblages were primarily related to depth beneath the streambed rather than local hydrochemical conditions, indicating only a limited effect of groundwater discharge on hyporheic communities in this stream. Overall, the chambers revealed finer spatial scale variation than methods used in previous published studies and allowed environmental and ecological characterisation at comparable spatial scales. Future studies using such chambers should seek to increase the number of measured covariates, to better understand the controls on invertebrate assemblages.

Interstitial velocity within spawning bed substrates is frequently used to predict salmonid embryo survival and often forms the basis of habitat assessment or sediment-based predictive models. In this study, the relationships between interstitial velocity, hyporheic dissolved oxygen (DO), and survival of Atlantic salmon Salmo salarembryos were examined in an experimental field study that incorporated natural complexity in the hyporheic environment. Hyporheic DO and interstitial velocity were not clearly related over the observed range of velocities. There was strong evidence of a relationship between survival and DO but only weak evidence of a relationship with interstitial velocity. Conceptual models of hyporheic environmental variation and salmonid embryo survival should include the appropriate range of environmental processes. Given the findings of this study, we suggest that interstitial velocity should not be used to assess or predict spawning habitat quality; direct measurements of DO offer a more defensible approach.

AbstractInterstitial velocity within spawning bed substrates is frequently used to predict salmonid embryo survival and often forms the basis of habitat assessment or sediment-based predictive models. In this study, the relationships between interstitial velocity, hyporheic dissolved oxygen (DO), and survival of Atlantic salmon Salmo salarembryos were examined in an experimental field study that incorporated natural complexity in the hyporheic environment. Hyporheic DO and interstitial velocity were not clearly related over the observed range of velocities. There was strong evidence of a relationship between survival and DO but only weak evidence of a relationship with interstitial velocity. Conceptual models of hyporheic environmental variation and salmonid embryo survival should include the appropriate range of environmental processes. Given the findings of this study, we suggest that interstitial velocity should not be used to assess or predict spawning habitat quality; direct measurements of DO offer a more defensible approach.

Over a 3.5 year period, levels of dissolved oxygen (DO) saturation were continuously monitored in surface waters and at depths of 150 and 300 mm in the hyporheic zone of a riffle in a montane stream where Atlantic salmon spawn. Throughout this period, DO in surface waters remained close to 100% saturation, but exhibited daily variations related to CO2cycling driven by diurnal patterns of respiration and photosynthesis. However, in the hyporheic zone, variations were much more dynamic over storm event, seasonal and inter‐annual timescales. At 300 mm, DO saturation was generally close to 100% during summer low flows, though levels occasionally fell during warm periods which appeared to be related to diffusion gradients caused by benthic respiration. Such DO decreases at low flows were much more common and marked at 150 mm. During wetter conditions, DO saturation at 300 mm fell to zero for prolonged periods; this is consistent with increased fluxes of groundwater discharging through the hyporheic zone. During the wettest periods this also affects DO saturation at 150 mm. However, during hydrological events, hyporheic water quality is ‘re‐set’ as head reversals cause streamwater ingress which results in transient periods of re‐oxygenation, which end during the hydrograph recession. This is consistent with stream‐ward hydraulic gradients being re‐established in riparian ground water as the stream stage falls. The connectivity between groundwater and streamwater through the hyporheic zone is driven by climatic conditions and is reflected in marked inter‐annual variability in water quality characteristics. In some cases, this variability may have implications for the ecology of the hyporheic environment—including the survival of salmon eggs—particularly if oxygen levels are affected. Copyright © 2009 John Wiley & Sons, Ltd.

The Girnock Burn is an Atlantic salmon (Salmo salar) spawning tributary of the river Dee, Aberdeenshire, Scotland. The dates, sexes and numbers of adult salmon entering the stream in the three months prior to spawning were determined between 1969 and 2005 using a permanent fish‐trap. During this time, the number of fish returning to spawn varied markedly. Here we analyze the whole of this unique long term data set in order to characterize and classify the hydrologic regimes of the pre‐spawning migration period and assess the extent to which these regimes help explain the timing and patterns of arrival of adult salmon into the stream. A range of flow parameters was calculated for the arrival period (September–November) for each of the 37 years. These parameters were used to ordinate and classify years according to their flow regimes. The analysis yielded six distinct groups or ‘flow regime types’ which separated principally in relation to flow magnitude and frequency parameters. The number of fish entering the burn on a given day was not significantly correlated to discharge on that day. However, patterns of arrival of fish differed markedly between years with different regime types, with the number of fish arriving on a given day related to patterns of discharge over the preceding part of the arrival period. Overall inter‐annual variability in entry corresponded to the defined regime types. In wetter years, fish entry to the stream usually starts relatively early and continues throughout the pre‐spawning period. In contrast, dry years may result in fish entry being delayed; this may result in lower numbers of spawning females entering the stream and sub‐optimal utilization of juvenile habitat in the following spring. Copyright © 2008 John Wiley & Sons, Ltd.

This paper quantifies patterns of discharge and temperature variation in the regulated river Lyon and the adjacent, unregulated river Lochay (Scotland) and assesses the importance of these patterns for benthic invertebrate community structure. Invertebrates were sampled at sites in each catchment in autumn, winter and spring during the 2002–2003 hydrological year. Metrics were used to characterize the discharge and temperature regimes in the period immediately preceding invertebrate sample collection. Metric values were then used in a canonical correspondence analysis (CCA) of the invertebrate sample data, in order to assess the significance of individual metrics and the overall importance of flow and temperature variability for community structure. The variance in the invertebrate data explained by this CCA was compared to that from a CCA using a range of environmental data from the sites (stream‐bed algal cover, channel hydraulic, sedimentary and water quality characteristics). This comparison allowed assessment of the relative importance of environmental variables versus hydrologic and thermal regimes.

This paper reports the findings of research designed to assess the ability of PHABSIM to predict Atlantic salmon Salmo salarspawning habitat in the Girnock Burn, a tributary of the River Dee in northeast Scotland. It used an 18‐year spawning data record to assess: (a) the ability of PHABSIM to predict between‐year differences in the availability of habitat at the study site; (b) the ability of PHABSIM to predict patterns of relative suitability across the site; and (c) the influence of different Habitat Suitability Indices (HSIs) on the model's predictions with respect to (a) and (b).

The spatial and temporal variability of groundwater–surface water (GW–SW) interactions in the hyporheic zone were investigated in a semi‐pristine upland salmon spawning catchment (Girnock Burn) in the Cairngorm Mountains, northeast Scotland. Stream and hyporheic water quality (200–300 mm depth) were monitored fortnightly at 16 spawning locations distributed throughout the catchment. Hydrochemical tracers were used to assess local GW–SW interactions. Stratified streambed incubators (50–300 mm) provided information on salmon embryo mortality at a sub‐set of ten locations. Hyporheic water quality varied both temporally and spatially according to local GW–SW interactions. It was possible to categorize sites into three broad typologies reflecting local stream–aquifer interactions: (1) groundwater‐dominated; (2) surface water‐dominated; and (3) sites exhibiting transient water table features. Groundwater upwelling occurred in areas where low permeability glacial moraine features caused substantive valley constriction. These locations were also conducive to accumulation of spawning grade gravels and consequently were utilized heavily by spawning salmon. Long residence groundwater was typically characterized by low dissolved oxygen (DO), of sufficiently low quality to be detrimental to salmon embryo survival. At sites dominated by surface water, hyporheic DO remained high throughout and rates of embryo survival were correspondingly high. Survival rates were also high at sites where hydrochemical characteristics indicated a transient water table. This is probably attributable to the hydrological conditions which resulted in increasing DO concentrations towards hatch time when embryo oxygen demand is at its maximum. The degree to which the findings of this study are directly applicable to other catchments is currently unknown. However, similar effects have been observed elsewhere, and based on the information presented here, there are clear implications for fisheries managers who may wish to consider the use of surface incubation facilities to negate the effects of low DO groundwater upwelling where it dominates available spawning habitat. It is suggested that future research should aim to integrate across spatial scales and disciplines to obtain a better understanding of the ways in which hillslope and riparian zone hydrology affect GW–SW interactions, hyporheic zone processes and stream ecology. © Crown copyright 2005. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

The locations used by spawning Atlantic salmon (Salmo salar L.) in a reach of the Girnock Burn, Scotland, were monitored over three successive years. Reach discharge was estimated for each spawning observation using a conversion factor applied to continuous flow data from a gauge located in the catchment. Data on the availability and use of different discharges were used to construct a discharge electivity index for the reach. The index was compared to output from a Physical HABitat SIMulation (PHABSIM) model of the reach. Spawning fish used relatively high discharges, with the highest electivity value being for a discharge approximately three times the reach median flow. The electivity index and the PHABSIM weighted usable area (WUA) versus discharge curve were similar across the low flow range and both suggested similar optimum discharges for spawning (1.1 and 1.4 m³ s⁻¹ respectively). However, electivity values suggested unsuitable conditions were reached at discharges greater than 1.4 m³ s⁻¹ whereas PHABSIM predicted relatively high WUA values at discharges up to 2 m³ s⁻¹. Electivity indices provide an insight into discharge selection that is not dependent on hydraulic simulations or assumptions about microhabitat (depth, velocity, substrate) preferences. Moreover, they can be used to assess discharge suitability in hydraulically complex streams where the one-dimensional hydraulic models used by PHABSIM may be inappropriate. However, unlike PHABSIM, they cannot be used to predict the suitability of flows outside observed discharge ranges and so are limited in their application. Further work is required to refine the methodology and assess its transferability to other streams. Nonetheless, indices may represent a useful tool that can be used to complement other methods of assessing instream flow needs. Copyright © 2002 John Wiley & Sons, Ltd.

The locations used by spawning Atlantic salmon (Salmo salarL.) in a reach of the Girnock Burn, Scotland, were monitored over three successive years. Reach discharge was estimated for each spawning observation using a conversion factor applied to continuous flow data from a gauge located in the catchment. Data on the availability and use of different discharges were used to construct a discharge electivity index for the reach. The index was compared to output from a Physical HABitat SIMulation (PHABSIM) model of the reach.

The spawning sites selected by female Atlantic salmon (Salmo salar)were surveyed over three consecutive years in the Girnock Burn, Aberdeenshire, Scotland. Discharge was calculated for each spawning site to assess within‐catchment variation in spawning discharge selection. In total, 428 incidents of female spawning activity were logged at 48 sites. Fish selected relatively high flows in which to spawn, with the lowest utilised discharge being equivalent to the burn's 50 percentile flow.

Polluted discharges from abandoned mines are a major cause of freshwater pollution in central Scotland, often contributing high Fe, SO₄^2- and acidity to receiving streams. The Central coalfield has been extensively mined for over a century and Polkemmet was the last colliery to close in 1985. Recent monitoring indicates that the rate of groundwater recovery is approximately 0.15 to 0.2 m per week. Without intervention, this trend would result in complete recovery by 2000 and probable discharge into the River Almond. Geochemical modelling indicates that pyrite oxidation, calcite dissolution and goethite precipitation are primarily responsible for the evolution of groundwater chemistry currently observed at Polkemmet. Predictive modelling using PHREEQE suggests that unregulated minewater discharges will have marked effects in the River Almond, with goethite being initially precipitated at a rate of up to 36 kg/day, dissolved sulphate concentrations ranging between 170 and 800 mg/l and pH being depressed to 6.5. Combined active lime flocculation and passive aerobic wetlands may be the most effective means of treating the predicted minewater discharges.

During the dry years between 1989 and 1994, inter‐basin water transfers from the Kielder system augmented flows in the River Derwent, and these flows substituted compensation releases from Derwent reservoir to retain storage for supply and recreational purposes.

Abstract A series of 63 significantly overweight adults (mean BMI = 48.8) underwent gastroplasty as surgical treatment designed to produce and maintain weight loss. A 6-month post-operative follow-up confirmed major weight loss in the sample, accompanied by significant improvements in psychological measures of anxiety, depression, difficulties with social interaction and perception of body shape. Pre-operative weight predicted amount of weight loss but not psychological outcome. Pre-operative psychological measures predicted both psychological outcome and weight loss. The need to avoid making assumptions about psychological outcome on the basis of weight loss outcome is identified. The nature of possible relationships between psychological variables and weight loss is considered.

The chemistry of bulk precipitation, throughfall, stemflow and soil waters beneath an oak wood (Quercus petraea) canopy and soil waters under moorland vegetation were measured at two sites on acid brown podzolic soils near Llyn Brianne in rural mid-Wales, UK. Between March 1986 and November 1988, precipitation was 4354 mm and annual interception losses from the oak canopy averaged 13% of incident precipitation. Throughfall and stemflow were more acid and concentrations of most solutes were increased 2- to 4-fold compared with bulk precipitation. Nitrate was the only solute retained within the tree canopy. Throughfall collected beneath patches of bracken on the forest floor was less acidic but contained substantially higher concentrations of major ions than bulk precipitation and oak throughfall. the moorland soil was more acidic, contained more exchangeable calcium but less exchangeable aluminium and potassium than the woodland soil. Soil waters beneath both vegetation types were acidic (mean pH range 4.5-4.9) and dominated by sodium and chloride. with the exception of calcium, soil water solute concentrations were greater beneath oak. These differences are ascribed to larger atmospheric inputs beneath the oak canopy compared with the shorter grasses, combined with the effect of differences in nutrient dynamics and water fluxes. Variations in soil water aluminium chemistry are explained in terms of ion exchange and podzolisa-tion processes. the water quality implications of increased upland afforestation of moorland by broadleaved trees are discussed.

The Lower Old Red Sandstones in northern Strathmore have favourable hydrogeological conditions for ground‐water development. A scheme was proposed to abstract water in the north Esk catchment in order to augment water supplies to local villages, and a production borehole was drilled into the Edzell Sandstones to give a design yield of 2420 m3/d. However, this scheme has been abandoned because of concern that the abstraction would significantly reduce the flow in a nearby stream which is an important salmonid fishery.

Spatially explicit knowledge of the origins of water resources for ecosystems and rivers is challenging when using tracer data alone. We use simulations from a spatially distributed model calibrated by extensive ecohydrological data sets in a small, energy‐limited catchment, where hillslope‐riparian dynamics are broadly representative of humid boreal headwater catchments that are experiencing rapid environmental transition. We hypothesize that in addition to wetness status, landscape heterogeneity modulates the water pathways that sustain ecosystem function and streamflows. Simulations show that catchment storage inversely controls stream water ages year‐round, but only during the drier seasons for transpiration and soil evaporation. The ages of these evaporative outputs depend much less on wetness status in the oft‐saturated riparian soils than on the freely draining hillslopes that subsidize them. This work highlights the need to consider local dynamics and time‐changing lateral heterogeneities when interpreting the ages, and thus the vulnerability, of water resources feeding streams and ecosystems in landscapes. Knowing how much time water spends in a landscape (its “age”) helps understanding how water travels through it. These dynamics inform of the stability of water resources for ecosystems and societies, and of their vulnerabilities under climate and land use changes. Water ages may vary depending on how wet or dry a location gets between seasons and years. We thus need to learn more about the demographics (“how much and how old?”) of the water used by plants, evaporated from soils, and flowing in streams, but it is often impossible to monitor the heterogeneity of water pathways within landscapes. Addressing this challenge, we used a numerical model built upon coupling ecohydrological processes and that maps landscape locations. We adjusted this model using multiple data sets in a catchment representative of humid boreal environments where climate and vegetation are rapidly changing. We found markedly different aging patterns between water escaping the system through the plants, soils, and stream, depending on water storage status. This changing duration of water movement also differs between the catchment as a whole and its parts. This method can be used to better understand the multiple ways in which water moves through landscapes, in current and future conditions. Age since precipitation displays inverse storage effect in stream, but not transpiration and soil evaporation, in a humid northern catchmentHysteresis between storage and the age of transpired water suggests cross‐season carryover, despite weak hydroclimatic seasonalityDownslope water subsidies result in valley bottom having weaker storage‐age relationships than seen in freely draining hillslopes

We used both time domain (deuterium) and source area (alkalinity) tracers to reduce uncertainty in simple conceptual rainfall‐runoff models applied to a larger (749 km2) heterogeneous catchment with both upland and lowland headwaters. Stepwise, tracer‐aided model development resulted in different model structures for the uplands and lowlands as representative elementary watersheds (REWs). These were differentiated by the parameterization of a nonlinear overland flow mechanism in the former, and the incorporation of high soil moisture storage capacity in the latter. Use of tracers and recession characteristics also helped to reduce parameter uncertainty and provided models that could simulate flows and tracer responses reasonably well over a full hydrological year. However, it was apparent that other processes (e.g., more complex mixing, fractionation, etc.) would need to be parameterized to explain the full variation in isotope dynamics. It is also evident that the information content of tracer data declines as the intensity of sampling decreases, particularly in the lowlands. The models of the REWs were coupled to provide plausible simulations of the up‐scaled flow and tracer response at the outfall of the 749 km2catchment, though the usefulness of source area tracers decreased markedly at this larger scale. Whereas the approach provides a step toward simple models that are likely to give the “right answer for the right reasons,” further improvements appear to require increased parameterization and/or higher‐resolution tracer data. Dominant runoff generation on larger scales is controlled by geologyTracers provide an integrated response and give answers at the scale of interestParameters in simple model structures can be constrained using tracer data